1. Field of the Invention
The present invention relates to computer-input technologies and more particularly, to a membrane circuit board and a light-emitting keyboard using the membrane circuit board, wherein the membrane circuit board comprises a lower layer, an upper layer, and a light-guiding spacer layer arranged between the lower layer and the upper layer, and the light-guiding spacer layer is formed with a tapered through hole that provides room for a triggering stroke for enabling a second circuit of the upper layer to electrically connect to a first circuit of the lower layer and to further produce a corresponding switching signal when the membrane circuit board is triggered by a key assembly, and thus, the light-emitting keyboard has a low profile characteristic.
2. Description of the Related Art
In the era of technological we live today, electronic products bring people a convenient environment. However, most electronic products need an input device for data input, such as mouse, keyboard, joystick, light gun, etc. However, with the creation of advanced electronic products, keys and buttons for data input also need to be changed to fit different requirements. Most today's keyboards provide a light-emitting function.
FIG. 6 illustrates a keyboard design according to the prior art. According to this design, the keyboard comprises a substrate A, a light guide plate B, a membrane circuit board C, at least one key assembly D, and at least one light-emitting component E. The light guide plate B is mounted at the top side of the substrate A. The membrane circuit board C is supported on the top surface of the light guide plate B. The at least one key assembly D is supported on the membrane circuit board C, each comprising a key cap D1 and a transparent elastic element D2. The elastic element D2 is set between the key cap D1 and the membrane circuit board C. The light-emitting component E is mounted at one lateral side of the light guide plate B beneath the membrane circuit board C. Thus, the light emitted from the light-emitting component E can go into the inside of the light guide plate B and then be guided out or transmitted by the light guide plate B toward the transparent elastic element D2 and the key cap D1. The membrane circuit board C comprises an upper layer with a bottom-sided circuit, a lower layer with a top-sided circuit, and a spacer layer set between the upper layer and the lower layer to keep the upper layer and the lower layer vertically apart. The spacer layer has through holes. When one key assembly D is pressed, the upper layer of the membrane circuit board C is forced to deform elastically, causing a part of the bottom-sided circuit to protrude into one through hole of the spacer layer into contact with the top-sided circuit of the lower layer of the membrane circuit board C and produce a corresponding switching signal.
When assembling the aforesaid prior art keyboard, place the light guide plate B on the substrate A, and then electrically connect each light-emitting component E to the membrane circuit board C, and then mount the membrane circuit board C on the light guide plate B, and then mount the at least one key assembly D on the membrane circuit board C.
Further, it is the market trend to crease computers and related peripheral apparatuses that have light, thin, short and small characteristics. Thus, keyboards must be made having a low profile characteristic to satisfy specialized market requirements. However, the keyboard has been around for decades, and its technology is very mature. The internal structure of the keyboard has been very simplified. Under the situation that there is no groundbreaking material research performed, it is the primary goal of manufacturers to create a keyboard having a low profile characteristic while maintaining the desired functions and structure.
FIG. 7 illustrates a self-luminous circuit board that is capable of emitting light and practical for use in a keyboard. This self-luminous circuit board comprising a printed circuit board F and a circuit layer G. The circuit layer G is embedded in the printed circuit board F, comprising a circuit layout for conducting the printed circuit board F. The printed circuit board F comprises a top substrate F1 and a bottom substrate F2. The top substrate F1 and the bottom substrate F2 have different thicknesses. The circuit layout of the circuit layer G is arranged on the junction between the top substrate F1 and the bottom substrate F2. The bottom substrate F2 is relatively thicker. The bottom substrate F2 works as a light guide board and comprises a light emitting portion F22 for diffusing light uniformly, and a light source F21 mounted therein for emitting light laterally. The light emitting portion F22 is located in the top surface of the bottom substrate F2. The light source F21 is mounted inside the bottom substrate F2.
This prior art design has the light source F21 mounted in the printed circuit board F, eliminating the use of an extra light-guiding board, and thus, the thickness and number of components of the product can be minimized to facilitate the implementation of the assembly process. However, because the implementation of the circuit layout of the circuit layer G needs to apply a certain amount of silver paste to the top substrate F1 and bottom substrate F2 of the printed circuit board F. When applying silver paste to the top substrate F1 and bottom substrate F2, the top substrate F1 and the bottom substrate F2 can be eroded, causing edge chipping or generation of undesired holes in the top substrate F1 and the bottom substrate F2. Further, when the light emitted from the light source F21 goes into the inside of the bottom substrate F2, the silver paste lines can cause a severe light leakage problem, lowering the luminous performance of the product, or leading to a defected product.
Therefore, it is desirable to provide a keyboard, which eliminates the drawbacks of large thickness, complicated assembly procedure and high cost.